In the prior art, a frame structure of Time Division-Long Term Evolution (LTE) includes the Frequency Division Duplex (FDD) Type1 and the Time Division Duplex (TDD) Type2.
In the frame structure of the FDD Type1 as illustrated in FIG. 1, a radio frame of 10 ms is divided into ten sub-frames with a length of 1 ms, each of which is consisted of two slots with a length of 0.5 ms.
In the frame structure of the TDD Type2 as illustrated in FIG. 2, a 10 ms radio frame is consisted of two half-frames with a length of 5 ms, each of which is consisted of five sub-frames with a length of 1 ms including four normal sub-frames and one special sub-frame. The normal sub-frames each are consisted of two 0.5 ms slots, and the special sub-frame is consisted of three special slots: an Uplink Pilot Time Slot (UpPTS), a Guard Period (GP) and a Downlink Pilot Time Slot (DwPTS). The LTE TDD Type2 is also referred to as TD-LTE.
In an existing synchronization solution of LTE, there are a “primary synchronization signal” and a “secondary synchronization signal” on a synchronization channel for cell searching. In the two frame structures, the LTE synchronization signals are located differently: the primary synchronization signal and the secondary synchronization signal adjoining together are located in the middle of the sub-frames 0 and 5 in the FDD Type1, as illustrated in FIG. 3; in the TDD Type2, the secondary synchronization signal is located at the end of the sub-frame 0 and the primary synchronization signal is located in the special sub-frame, i.e., the third symbol of the DwPTS, as illustrated in FIG. 4.
Thus in the two frame structures, the absolute locations of the synchronization signals in a radio frame are different, and more importantly the relative locations of the primary synchronization signal and the secondary synchronization signal are different: the primary synchronization signal and the secondary synchronization signal adjoin together in the FDD and are spaced by a temporal interval of two symbols in the TDD. Since the synchronization signals are the first signals to be detected by a user equipment searching for a cell, such a design with a varying relative location may enable the user equipment to detect an FDD or TDD duplex mode of a network at the very beginning of an access to the network.
The user equipment with an access to the network has to perform a corresponding synchronization process for time slot synchronization and symbol synchronization, particularly as follows:
The user equipment receives a primary synchronization signal from a base station and performs cell synchronization according to the primary synchronization signal and also locates a 5 ms temporal reference according to a primary synchronization code and adjusts a carrier frequency. The user equipment receives a secondary synchronization signal from the base station and detects a cell identifier according to the secondary synchronization signal, and the secondary synchronization signal is a different pilot sequence adopted for respective cells.
In a random access process, the user equipment detects reception power of a pilot sequence received in the downlink and then acquires a path loss of a downlink channel according to predefined transmission power and determines transmission power from the path loss and reception power required for the base station.
Since a carrier frequency in the uplink is different from that in the downlink in an FDD system, there is no reciprocity between the uplink and the downlink, and the user equipment can not estimate channel attenuation in the uplink from reception power of the received primary and secondary synchronization signals transmitted in the downlink, so that transmission power of the last Physical Random Access Channel (PRACH) preamble is controlled in a power ramping mode of PRACH power control in the prior art, that is, firstly transmission power is estimated taking downlink attenuation as uplink attenuation and a preamble is transmitted, and if there is no feedback for the last preamble, then the power is boosted for another transmission. A calculation formula of PRACH power control is:P=min{Pmax, PL+P0,pre+Δpre+(Npre−I)dPrampup}
Where P is transmission power of the preamble of the user equipment; Pmax is the maximum transmission power of the user equipment; PL is the value of a downlink path loss measured by the user equipment; P0,pre is a cell specific parameter, i.e., target reception power of the preamble at the eNodeB (base station) dynamically ranging from −120 dBm to −90 dBm with a resolution of 2 dB; Δpre is a correction value for a varying preamble length; Npre is the number of times that the user equipment transmits the preamble; and dPrampup is a cell-specific power ramping step for retransmission of the preamble and takes possible values of 0, 2, 4 and 6 dB. The user equipment boosts the transmission power continuously by the step of dPrampup as the number of times that the user equipment transmits the preamble is increased, thereby achieving the effect of power ramping.
In the existing FDD system, the user equipment can not acquire accurately any uplink path loss to further determine the transmission power of the RACH access preamble and consequently has to trigger the power ramping flow to adjust the transmission power prior to the random channel access, thus complicating and prolonging the random link access process.